Enameling oven



2 Sheets-Sheet l ENAMELING OVEN c. s. PRESCOTT ETAL wm lu u l h" Aug. 1, 1950 Filed June 17 1946 INVENTORS Charla .5. Present, Faber: M Brawn ATTORNEYJ Aug. 1, 1950 c. s. PRESCOTT EI'AL ENAMELING OVEN Filed June 17, 1946 2 Sheets-Sheet 2 Charla: 62 karat! Reba/t Mirna/1 ATTORNEYS Patented Aug. 1, 1950 ENAMELING OVEN Charles S. Prescott and Robert M. Brown, Muskegon, Mich., assignors to Anaconda Wire and Cable Company, a corporation of Delaware Application June 17, 1946, Serial No. 677,290

9 Claims. (01. 263-15) This invention relates to enamelling ovens, and

particularly to ovens of the character employed for baking enamel imulating coatings on magnet wires. The invention provides an enamelling oven embodying-a number of new and improved features of construction, including provision for burning the enamel fumes volatilized in the oven, and provision for maintaining the oven temperature at a higher value near the wire-exit end than near the wire-entrance end.

Magnet wires often are insulated with a thin film of enamel baked on the wire. In the manufacture of this product, the wire first is coated with a film of wet enamel, usually by causing it to dip beneath the surface of a pool of enamel, and then is passed through a fairly long baking oven. The oven is maintained at a temperature high enough to drive off the solvents and other volatile constituents of the wet enamel and to harden the residual enamel film on the wire.

Generally a considerable number of coats of enamel must be applied to the wire to build up an enamel film thick enough to possess adequate electrical insulating properties. As many as twelve or more coats of enamel often are applied to the wire, especially when the common oleoresin enamel long known to the industry is em ployed. It is therefore common practice to pass the wire back and forth through the oven a number of times, a fresh coat of enamel being applied to the wire each time it emerges from the oven and before it re-enters.

In heretofore known enamelling operations the solvents, thinners, and other volatile constituents of the enamel that are driven off as a fume in the oven pass as fume through exhaust flues, through which they are vented to the atmosphere. These fumes impart a characteristic odor to wireenamelling plants, and the odor is considered objectionable by some. More objectionable than the odor from an operating standpoint, however, is the fact that the less volatile constituents of the fume condense in the exhaust flues. After only a few weeks of continuous operation, such a heavy deposit of tarryfume condensate collects in the fines that it is necessary to shut down the oven and clean out the flues. This is an expensive operation, both because the oven is idle while it is being carried out, and because it is necessarily a handperformed job.

The present invention overcomes this objectionable characteristic of heretofore known enamel-baking ovens, especially wire-enamelling ovens, by providing for burning substantially H completely the combustible enamel fume products volatilized in the oven. In accordance with this feature of the invention, provision is made for withdrawing the fume products from the oven chamber wherein they are volatilized, for burning the products at a point outside the oven chamber, and for passing the burned products to an exhaust flue.

A further disadvantage inherent in wire-enamelling ovens of the character heretofore customarily employed results from the fact that the wire is passed back and forth through the oven a number of times. Due to the fact that wire is both entering and leaving the oven at each end, it has been considered the best practice to heat the oven by means of heated air admitted near the center of the oven chamber and exhausted therefrom at each end. As a result, the central portion of the oven is generally at a somewhat higher temperature than either end. The wire is heated through a gradually increasing temperature gradient from the point it enters the oven to near the center, and thereafter it passes through a decreasing temperature gradient. We have found that in this latter section of the furnace the enamel is not as efficiently or as effectively baked as when the temperature gradient increases continually from the entrance to the exit end of the oven. This apparently is due to the fact that as volatile constituents of the enamel are driven from the wire, a gradually increasing temperature is advantageous to expel the residual volatile constituents and to bake the enamel to optimum hardness. Further the hot air flowing in part concurrently with the wire sweeps the volatile fumes along with the wire, and these fumes impede curing of the enamel film.

Accordingly, the present invention provides for passing wires in only one direction through the oven and maintaining the temperature within the oven at a higher value near the wire-exit end than near the wire-entrance end. A convenient arrangement according to the invention for accomplishing this result is to provide a combustion chamber separate from but arranged in heat-exchange relation with the oven chamber adjacent the wire-exit end thereof. Provision is made for burning fuel in the combustion chamber, and means are provided for introducing the hot combustion gases and heated air into the oven chamber near its wire-exit end. The combustion gases, admixed with volatile and combustible enamel fume products, are then withdrawn from the oven chamber near its wire-entrance end. These gases then may be passed to a second combustion chamber to burn the combustible enamel products prior to passing the gase to an exhaust flue. The gas flow in the oven is counter-current to the flow of wires, so that the high temperature portion of the oven adi acent the wire-exit end is kept free of volatile fumes which would impede curing of the enamel The combustion chamber wherein the combustible enamel fume products are burned may advantageously also be arranged separate from but in heat-exchange relation with the oven chamber adjacent its wire-exit end. The heat released in the combustion of the enamel fume products then may contribute to maintaining the desired relatively high temperature adjacent the wire-exit end of the oven chamber.

In order to insure substantially complete combustion of the enamel fume products, it is advantageous to pass them through a flame of burning fuel issuing from a burner adjacent the entrance to the fume-burning combustion chamber. Complete combustion of the fume may be assured by providing a perforated refractory combustion wall against which the igniting flame plays and through which the fume must pass.

When using ovens arranged in accordance with the invention for passing wires in only one direction, it is advantageous to employ two such, ovens set up parallel to each other and together forming a single operating unit. The wire then may be passed in one direction through one oven and back in the opposite direction through the other oven. A fresh coat of enamel may be applied to the wire each time it enters each oven, and as many coats may be applied in this fashion as desired. When a pair of ovens is thus employed, it

by conserving floor space and facilitating flue and other connections to the ovens and their associated components.

In order to secure maximum economy and efilciency in burning fuel for heating the oven, provision advantageously is made for introducing combustion air to the combustion chamber by passing it through an air inlet conduit which leads through'the combustion chamber, thereby preheating the air prior to introducing it into the combustion zone. It is also advantageous to provide means for distributing the combustion air and combustion gases uniformly across the width of the oven to insure uniform heating across its width.

The foregoing and other features of the invention are described more fully below in conjunction with the oven structuresshown in the accompanying drawings, in which Fig. 1 is an elevation, partly in longitudinal section, of wire-enamelling oven equipment according to the invention:

Fig. 2 is a longitudinal horizontal section taken substantially along the broken line 22 of Fig. l; Fig. 3 is a cross section taken substantially along the broken line 33 of Fig. 1; and

Fig. 4 is an end-view taken along the line 4-4 of Fig. 1, showing the passage of a plurality of wires from the lower to the upper oven chamber.

The wire-enamelling equipment shown in Fig. 1 comprises two oven structures l and I I mounted parallel and vertically one above the other. These two oven structures are each substantially the same in construction, except that they are reversed end for end. The following detailed description of the oven construction is therefore 4 directed primarily to the. lower oven structure l0 shown in longitudinal section in Fig. 1, but it is applicable also to the upper oven structure H. The oven structure I. is housed within a steel shell i2 supported by suitable framework It and lined at the top, bottom, sides and ends with refractory heat-insulating brickwork H. A long and rather wide but shallow oven chamber II is provided within the oven structure. This oven chamber is closed at its ends by refractory-lined steel channels l6 defining narrow slots i I extending the. width of the oven chamber for the passage of wires into and out of the oven chamber. The refractory-dined channels Ii between which these slots are defined advantageously are removable so that access may be had conveniently to the interior of the oven chamber when it is first strung with wires, and when repair work is necessary.

A wire I 8 on which a coat of enamel is to be baked is first dipped beneath the surface of a pool of enamel l9, and then is passed through the oven chamber in the lower oven structure II. The baked enamel-coated wire 20 emerging from this oven chamber then is passed upwardly and dipped beneath the surface of a second pool of enamel 2| to apply a second coat, after which it is passed through the upper oven structure II in the reverse direction to its passage through the lower oven. The wire emerging from the upper oven structure ll may be passed down into the first pool of enamel I! to apply still another coat, and the wire may be recycled through the two ovens any desired number of times to apply any desired number of coats of enamel. After the last coat has been applied and baked on the wire, the finished wire 22 is led off to be wound on a spool for its further disposition.

Arranged beneath the oven chamber l5 adiacent its wire-exit end is a combustion chamber 23. This combustion chamber is sepa rated from the oven chamber by a relatively thin sheet of steel 24 or other material of good heat conductivity, so that the combustion chamber is in heat-exchange relation with the oven chamber.

Combustion air is introduced by a blower through an air inlet conduit 25 which passes through the combustion chamber 23 to the rear of an air-distributing chamber 26 located behind the combustion chamber. The air inlet conduit terminates in an air-distributing header 2?, by which the air is directed back into the air-distributing chamber. serves to insure substantially uniform distribution of the air across the width of the oven, and a perforated brick baffle 28 may be provided to facilitate this distribution.

A burner 29 extending across the width of the combustion chamber is arranged where the air-distributing chamber 25 adjoins the combustion chamber 23. Fuel (such as gas) premixed with additional combustion air is introduced by a blower 30 (Fig. 2) supplied with air and fuel gas in carefully controlled proportions by proportionin' equipment 3| and driven by a motor 32. The amount of combustion air admitted to the combustion chamber 23 (through the air in let conduit 25 and with the fuel blown into the burner 29) is always considerably in excess of the amount required to burn the fuel, so that considerable heated air enters with the combu tion gases into the oven and residual combustion air is available in the gases for subsequent burning of the enamel fume products.

This distributing chamber more hot gases pass to the end of the combustion chamber adjacent the wire-exit end of the oven chamber, and there they pass through an opening 35 into the oven chamber itself. A deflector plate 86 directs the gases back through the ove chamber toward the wire-entrance end. a

As the hot combustion gases pass back through the length of the oven chamber, enamel solvent, thinner and other combustible fume products volatilized from the enamel coated wires become admixed with them. The resulting mixture of combustion gases, combustible enamel fume products, and excess air is withdrawn from the oven chamber through an opening 31, adjacentits wire-entrance end, into a passage 38 above the oven chamber and separated from it by a heat-insulated partition 39. 'This passage terminates before afume combustion chamber III, at the head of which is a burner 4! arranged to play a flame of burning fuel against a perforated refractory combustion wall 42. The enamel fume products present in the gas mixture are ignited by the flame and burn with the excess air in the combustion chamber 40.

A thin partition 43 of good heat conductivity (such as a steel sheet) separates the fume combustion chamber 40 from the oven chamber adjacent its wire-exit end, and accordingly the heat of combustion of the fume products, and the heat of combustion of the fuel burned as it issues from the burner ll, is transferred in large part to the oven chamber, thus contributing to maintaining it at the desired enamel baking temperature. The final combustion products leaving the combustion chamber 40 enter a flue H by which they are conveyed to a stack 45 and are discharged to the atmosphere.

The natural draft of the stack 45 may be sufficient to effect complete discharge of the combustion gases from the oven, but a fan or blower may be used to force and regulate the draft if desired. The oven structure is well insulated and but little heat islost with the wires leaving the oven. Consequently a low rate of flow of hot combustion gases through the oven chamber suffices to keep it at the operating temperature. When the rate of gas flow through the oven is low, as is generally the case, and with the fuel and combustion gases introduced under a slight pressure above atmosphere, a light stack draft serves to withdraw all the combustion gases without any appreciable flow of air or combustion gases into or out of the oven chamber through the wire-passage slots H.

By burning the enamel fume products substantially completely in the fume-combustion chamber 40, these products are converted to noncondensible combustion gases which pass freely through the fines and stack. Consequently there is no significant collection of condensed tarry fume products in the flues and no heed for frequently shutting down the furnace to clean the flue. In addition the odor that attends the discharge of enamel fumes to the atmosphere is eliminated. Substantially complete combustion of the enamel fume products is assured by the arrangement of the burner 4| to play a flame over substantially the entire surface of the combustion wall 42. ,Since the fume products in admixture with the combustion gases from the oven chamber must pass through this flame and through the heated combustion wall, and since an excess of air is present with the combustion gases, ignition and combustion of virtually all of the fume products is assured, even though concentration of the fume products in the combustion gases from the oven chamber may be quite low.

The provision for admitting the hot combustion gases into the oven chamber near its wireexit end, and for withdrawing these gases from near the wire-entrance end of the oven chamber, results in maintaining the temperature in the oven chamber at a higher value near the'wireexit end than near the wire-entrance end. A temperature gradient which gradually increases from the wire-entrance end to the wire-exit end thus is maintained within the oven chamber.

As the wire advances through the oven chamber, therefore, it is baked at progressively higher temperatures, resulting in efiicient and essentially uniform elimination of volatile enamel constituents and efficient baking of the residual enamel film.

Maintenance of a higher temperature at the wire-exit end of the oven chamber than at the wire-entrance end is assisted by the arrangement of the primary combustion chamber 23 below but in heat-exchange relation with the wireexit end-section of the oven chamber. It is further assisted by the arrangement of the fume combustion chamber In above and in heat-exchange relation with this same end-section of the oven chamber. In addition, the combustion of the enamel fumes in a combustion chamber in heat-exchange relation with the oven chamber leads to savings in the amount of fuel required t: bgsburned in the primary combustion cham- The temperature within the oven chamber may be controlled automatically by a thermocouple 46 extending into the oven chamber and suitably connected in an electric control circuit governing operation of the motor 32, thereby controlling the amount of fuel delivered through the burner 28 at the head of the combustion chamber 23. A second thermocouple I! for actuating a recording thermometer may also extend into the oven chamber to give a visual and permanent record of the temperature prevailing within the oven chamber.

Heat-insulation of the partition 39 separating the oven chamber from the passage 38 through which combustion gases are withdrawn from the oven chamber reduces heat transfer through the partition and therefore reduces the possibility of cooling the undersurface of this partition to the extent that enamel fumes will condense on it.

Although a single oven constructed as described above could be employed even for applying a number of coats of enamel to the wire (by passing the wire after it emerges from the oven back along'the outside of the oven to the wireentrance end), it is generally most efficient and therefore preferred to employ two ovens mounted parallel to each other, as are the oven structures In and ii shown in the drawings. The wire being enamelled may then be cycled forward through one oven and back through the other as many times asdesired to apply any desired number of coats of enamel. Mounting the two ovens as shown in the drawings, one vertically above the other, is particularly advantageous as considerable floor space is thereby saved.

Experience with enamelling ovens of the character described herein has shown that these ovens may be operated at a considerably higher rate than the conventional ovens heretofore employed. The increased capacity of the new ovens appears to be due to the fact that the temperature gradient which increases gradually in the direction of wire travel all the way from one end of the oven chamber to the other results in more efiicient volatilizationof enamel solvents and thinner and more emcient baking of the residual enamel film than has been achieved in ovens heretofore known. Moreover, since the volatilized fumes are swept back by the entering hot gases from the high temperature end of the oven, they do not impede curing of the enamel film. Consequently wire may be passed through the new oven at a higher speed than through the older type ovens, without impairing the quality of the enamelled wire product. Further, since the volatilized fume products are burned substantially completely, it

' is unnecessary to shut down the oven at fairly frequent intervals for pmposes of cleaning out tarry enamel fume condensate. This reduction in the amount of time during which the ovens must be shut down further contributes to an in crease in the amount of wire that can be enamelled over a period of say several weeks or months.

We claim:

1. An enamelling oven comprising an oven chamber, means for introducing hot fume-free and soot-free combustion gases into one end of the oven chamber and into contact with an enamel-coated wire therein, means for Withdrawing the combustion gases admixed with volatile and combustible enamel fume products from the other end of the oven chamber, means for burning the fume products after their withdrawal from the oven chamber, an exhaust flue, and means for passing the combustion gases and the burned enamel products directly to the flue without again entering the oven chamber wherein the enamelcoated wire is baked.

2. An enamelling oven comprising an oven chamber, a fuel burner and combustion chamber situated beneath the oven chamber, means for introducing hot fume-free and soot-free combustion gases from the combustion chamber into one end of the oven chamber and into contact with an enamel-coated wire therein, means for withdrawing the combustion gases admixed with volatile and combustible enamel fume products from the other end of the oven chamber to a second combustion chamber above the oven chamber, a fume burner in said second combustion chamber for igniting and burning the fume products after their withdrawal from the oven chamber, an exhaust flue, and means for passing the burned fume products directly to said flue without passing through the oven chamber.

3. A wire-enamelling oven comprising an oven chamber, means for introducing enamel-coated wire ino the oven chamber at one end thereof and for withdrawing the wire at the other end, a first combustion chamber, means for introducing hot fume-free and soot-free combustion gases from said combustion chamber into the oven c amber near its wire-exit end, means for withdrawing the combustion gases admixed [with volatile and combustible enamel fume products from the oven chamber near its wire-entrance end, a second combustion chamber, means for passing the combustion gases and fume products to said second combustion chamber, means for igniting and burning the fume products in the second combustion chamber, an exhaust flue, and means for passing the ignited and burned fume products directly to said flue without reentering the oven chamber wherein the enamel-coated wire is baked.

4. A wire-enamelling oven according to claim 3, in which the first combustion chamber is arranged in heat-exchange relation with the oven chamber adjacent its wire-exit end.

5. A wire-enamelling oven according to claim 3, in which the second combustion chamber is arranged in heat-exchange relation with the oven chamber adjacent its wire-exit end.

6. In a wire-enamelling oven, an oven chamber, means for introducing enamel-coated wire into one end of the oven and for withdrawing the wire from the other end thereof, a first combustion chamber arranged in heat-exchange relation with the oven chamber adjacent the wireexit end thereof, means for burning fuel gas in said combustion chamber, means for passing fume-free and soot-free fuel gas combustion products from said combustion chamber into one end of the oven and into contact with the enamelcoated wire therein, a second combustion chamher also arranged in heat-exchange relation with 'the oven chamber adjacent the wire-exit end thereof, and means for passing said combustion gases admixed with volatilized combustible enamel fumes from the opposite end of the oven into said second combustion chamber and for burning said fumes therein, said combustion chambers being arranged so as to maintain the temperature in the oven chamber higher at the wireexit end thereof than at the wire-entrance end.

7. In an enamelling oven including an oven chamber in which combustible enamel fume products are volatilized into the oven atmosphere, the improvement comprising means for heating the oven in part at least by hot combustion gases admitted into the oven'chamber, means for withdrawing the combustion gases admixed with the enamel fume products to a combustion chamber separate from the oven chamber, a perforate refractory combustion wall within said combustion chamber and extending transversely thereacross, a burner arranged to play a flame on a face of said combustion wall, and means directing the mixture of combustion gases and fume products into contact with the flame substantially at a right angle to the combustion wall and through the perforations thereof, whereby the fume products are ignited and burned.

8. In an enamelling oven including an oven chamber, means for heating the oven chamber comprising a combustion chamber separate from the oven chamber, an air-distributing chamber behind but adjoining the combustion chamber, an air inlet passage extending through the combustion chamber to the rear of the air-distributing chamber, means for directing air issuing rom the inlet passage back through the distributing chamber and for insuring uniform distribution of the air across the width of the chamber, and a burner extending across the width of the combustion chamber where it adjoins the air-distributing chamber and arranged to direct a flame through the combustion chamber over the air inlet passage and countercurrent to the flow of air through said passage.

9-. In an enamelling oven including an oven chamber, means for heating the oven chamber 76 comprising a combustion chamber separate from the oven chamber but disposed in heat-exchange relation therewith, an air-distributing chamber behind but adjoining the combustion chamber, an air inlet passage extending through the combustion chamber to the rear of the air-distributing 5 chamber, means for directing air issuing from the inlet passage back through the distributing chamber and for insuring uniform distribution of the air across the width of the chamber, a burner extending across the width of the combustion chamber where it adjoins the air-distributing chamber and arranged to direct a flame through the combustion chamber over the air inlet passage and countercurrent to the flow of air through said passage, battles in the combustion chamber arranged to insure uniform distribution of the hot combustion gases across the width of the combustion chamber, and means for introducing the hot combustion gases from the combustion chamber into the oven chamber.

CHARLES S. PRESCOTT. ROBERT M. BROWN.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,045,915 Turner Dec. 3, 1912 1,101,281 Holmes June 23, 1914 1,444,079 Maring Feb. 6, 1923 1,615,418 Walker et a1 Jan. 125, 1927 1,682,123 Hanfl Aug. 28, 1928 1,699,349 Dailey Jan. 15, 1929 1,947,545 Pugh Feb. 20, 1934 1,947,546 Reading Feb. 20, 1934 1,947,547 Fruth Feb. 20, 1934 2,005,580 Ferre June 18, 1935 2,059,441 Converse Nov. 3, 1936 2,087,145 Harris July 13, 1937 2,328,078 Kugier Aug. 31, 1943 

